fix(workflow): Take back LLM streaming output after IF-ELSE

[laipz8200]

Checklist:

Important

Please review the checklist below before submitting your pull request.

• Please open an issue before creating a PR or link to an existing issue
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods

Description

• Removed unnecessary type assignment logic for streamlined processor handling.
• Simplified checking node types by using direct enum references.
• Enhanced generator routing by eliminating redundant dictionary iterations.
• Improved code readability and maintainability with abstract base class refinement.
• Used Sequence instead of list for type consistency in value selectors.

Fixes #9852

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update, included: Dify Document
• Improvement, including but not limited to code refactoring, performance optimization, and UI/UX improvement
• Dependency upgrade

Testing Instructions

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• Test A
• Test B